The present invention relates to a process to prepare semi synthetic statins, to intermediates formed during said process and to highly purified simvastatin produced by the process.
Statin drugs are currently the most therapeutically effective drugs available for reducing the level of LDL in the blood stream of a patient at risk for cardiovascular disease. This class of drugs includes lovastatin, simvastatin, pravastatin, compactin, fluvastatin and atorvastatin.
Simvastatin is the common medicinal name of the chemical compound butanoicacid, 2,2-dimethyl-,1,2,3,7,8,8a-hexahydro-3,7-dimethyl-8-[2-(tetrahydro-4-hydroxy-6-oxo-2H-pyran-2-yl)-ethyl]-1-naphthalenyl ester, [1S*-[1a,3a,7b,8b(2S*,4S),-8ab]]. (CAS Registry No. 79902-63-9.) The molecular structure of simvastatin is shown below with atoms labeled to indicate numbering of the atoms. 
Lovastatin is the common medical name of the chemical compound [1S-[1xcex1(R*),3xcex1,7xcex2;8xcex2(2S*,4S*),8axcex2]]-1,2,3,7,8,8a-hexahydro-3,7-dimethyl-8-[2-(tetrahydro-4-hydroxy-6-oxo-2H-pyran-2-yl ethyl]-1-naphthalenyl 2-methylbutanoate. (CAS Registry No. 75330-75-5.) The molecular structure of lovastatin is shown below with atoms labeled to indicate numbering of the atoms. 
Lovastatin possess a 2-methylbutyryl ester side chain at the 8-position of the hexahydronaphthalene ring system. In contrast, simvastatin possess a 2,2-dimethylbutyryl side chain at the 8-position of the hexahydronaphthalene ring system. It is known that simvastatin is a more effective agent than lovastatin for reducing the level of LDL in the blood stream.
The prior art discloses methods for converting lovastatin to simvastatin. U.S. Pat. No. 4,582,915, incorporated herein by reference, discloses converting mevinolin, compactin and dihydro- and tetrahydro derivatives thereof to more active HMG-CoA reductase inhibitors by C-methylation of the natural 2(S)-methylbutyryloxy side chain to form a 2,2-dimethylbutyryloxy side chain.
U.S. Pat. No. 5,223,415 incorporated herein by reference, discloses the enzymatic hydrolysis of lovastatin acid, by treating lovastatin acid with Clonostachys compactiuscula ATCC 38009 or ATCC 74178, or a cell-free extract derived therefrom. The product is an inhibitor of HMG-CoA reductase and thus useful as anti-hypercholesterolemic agents. The product also serve as an intermediate for preparation of other HMG-CoA reductase inhibitors.
U.S. Pat. No. 4,293,496 incorporated herein by reference, discloses removal of the 2-methylbutyryl side chain by base hydrolysis of the ester of lovastatin with an alkali metal hydroxide, preferably LiOH. The products are useful as intermediates in the synthesis of antihypercholesterolemia agents.
U.S. Pat. No. 4,444,784, incorporated herein by reference, discloses the introduction of a new side chain to hydrolyzed lovastatin.
U.S. Pat. No. 5,159,104, incorporated herein by reference, discloses the formation of simvastatin, by the sequential acylation of a diol lactone to form a bis acylated intermediate followed by selective deacylation and lactone ring closure to form simvastatin.
The present invention provides substantially pure simvastatin which comprises less than about 0.1 weight % simva-oxolactone.
The present invention also provides substantially pure simvastatin which comprises less than about 0.1 weight % anhydrosimvastatin.
The present invention also provides substantially pure simvastatin which comprises less than about 0.1 weight % simvastatin dimer.
The present invention also provides substantially pure simvastatin which comprises less than about 0.1 weight % dihydrosimvastatin.
The present invention also provides substantially pure simvastatin which comprises less than about 0.1 weight % at least one compound selected from the group consisting of simva-oxolactone, anhydrosimvastatin, simvastatin dimer and dihydrosimvastatin.
The present invention also provides a pharmaceutical composition comprising substantially pure simvastatin and less than about 0.1 weight % simva-oxolactone.
The present invention also provides a pharmaceutical composition comprising substantially pure simvastatin and less than about 0.1 weight % anhydrosimvastatin.
The present invention also provides a pharmaceutical composition comprising substantially pure simvastatin and less than about 0.1 weight % simvastatin dimer.
The present invention also provides a pharmaceutical composition comprising substantially pure simvastatin and less than about 0.1 weight % dihydrosimvastatin.
The present invention also provides a pharmaceutical composition comprising substantially pure simvastatin and less than about 0.1 weight % of at least one compound selected from the group consisting of simva-oxolactone, anhydrosimvastatin, simvastatin dimer and dihydrosimvastatin.
According to another aspect, the present invention relates to a process for the formation of highly purified simvastatin from lovastatin, comprising the steps of: lactone ring opening by reacting lovastatin with an amine to form an amid; protecting a 1,3-diol moiety with a protecting group; removing a 2-methylbutyryl group attached by an ester linkage through an oxygen at position 8 of a hexahydronaphthalene ring; attaching a 2,2-dimethylbutyrate group by forming an ester linkage to a hydroxyl at position 8; removal of a protecting group; conversion of the amid to an acid salt; and, lactone ring closing to form simvastatin.
According to another aspect, the present invention relates a process for the formation of a semisynthetic statin of Formula I, 
from a statin of Formula II, 
which comprises the steps of: lactone ring opening by reacting the statin of Formula II with an amine to form an amid; protecting a 1,3-diol moiety with a protecting group; removing a 2-methylbutyryl group attached by an ester linkage through an oxygen at position 8 of a hexahydronaphthalene ring; attaching a 2,2-dimethylbutyrate group by forming an ester linkage to a hydroxyl at position 8; removal of the protecting group; conversion of the amid to an acid salt; and, lactone ring closing to form the semisynthetic statin of Formula I wherein R1 and R2 are both acyl groups linked to the oxygen through an ester bond and R3 and R4 are independently selected from the group consisting of xe2x80x94H, xe2x80x94OH, xe2x80x94C1-10 alkyl, xe2x80x94C6-14 aryl, and xe2x80x94C6-14 aryl-C1-3.
The present invention provides substantially pure simvastatin which comprises less than about 0.1 weight % simva-oxolactone.
The present invention also provides substantially pure simvastatin which comprises less than about 0.1 weight % anhydrosimvastatin.
The present invention also provides substantially pure simvastatin which comprises less than about 0.1 weight % simvastatin dimer.
The present invention also provides substantially pure simvastatin which comprises less than about 0.1 weight % dihydrosimvastatin.
The present invention also provides substantially pure simvastatin which comprises less than about 0.1 weight % at least one compound selected from the group consisting of simva-oxolactone, anhydrosimvastatin, simvastatin dimer and dihydrosimvastatin.
The present invention also provides a pharmaceutical composition comprising substantially pure simvastatin and less than about 0.1 weight % simva-oxolactone.
The present invention also provides a pharmaceutical composition comprising substantially pure simvastatin and less than about 0.1 weight % anhydrosimvastatin.
The present invention also provides a pharmaceutical composition comprising substantially pure simvastatin and less than about 0.1 weight % simvastatin dimer.
The present invention also provides a pharmaceutical composition comprising substantially pure simvastatin and less than about 0.1 weight % dihydrosimvastatin.
The present invention also provides a pharmaceutical composition comprising substantially pure simvastatin and less than about 0.1 weight % of at least one compound selected from the group consisting of simva-oxolactone, anhydrosimvastatin, simvastatin dimer and dihydrosimvastatin.
Method for Producing a Highly Purified Simvastatin
According to another aspect, the present invention relates to a process for the formation of highly purified simvastatin from lovastatin, comprising the steps of: lactone ring opening by reacting lovastatin with an amine to form an amid; protecting a 1,3-diol; removing a 2-methylbutyryl group attached by an ester linkage through an oxygen at position 8 of a hexahydronaphthalene ring; attaching a 2,2-dimethylbutyrate group by forming an ester linkage to a hydroxyl at position 8; removing the protecting; conversion of the amid to an acid salt; and, lactone ring closing to form simvastatin.
The conversion of lovastatin to simvastatin as provided by the invention is shown in Scheme I. 
The lactone ring opening step is preferably performed by reacting the lactone with ammonia, a primary amine, or a secondary amine. Preferably, the lactone ring opening step is performed by reacting the lactone with an amine selected from the group consisting of n-butyl amine, cyclohexylamine, piperidine and pyrrolidine.
Potential impurities which can be formed during the synthesis of simvastatin are shown in Scheme II. 
Preferably, the substantially pure simvastatin synthesized by the method of the invention comprises less than about 0.1% weight simva-oxalactane.
Preferably, the substantially pure simvastatin by the method of the invention comprises less than about 0.1% weight anhydrosimvastatin.
Preferably, the substantially pure simvastatin synthesized by the method of the invention comprises less than about 0.1% weight dihydrosimvastatin.
The present invention also provides substantially pure simvastatin which comprises less than about 0.1% simvastatin dimer.
Optionally, the substantially pure simvastatin synthesized by the method of the invention may be synthesized from an of impure mixture of lovastatin comprising as much as about 30% impurities.
Method for Producing a Highly Purified Statin
According to another aspect, the present invention relates to a process for the formation of a semisynthetic statin of Formula I, 
from a statin of Formula II, 
which comprises the steps of: lactone ring opening by reacting the statin of Formula II with an amine to form an amid; protecting a 1,3-diol; removing a R1 group attached by an ester linkage through an oxygen at position 8 of a hexahydronaphthalene ring; attaching an R2 group by forming an ester linkage to a hydroxyl at position 8; removing the protecting group; conversion of the amid to an acid salt; and, lactone ring closing to form the semi synthetic statin of Formula I, wherein R1 and R2 are both acyl groups linked to the oxygen through an ester bond and R3 and R4 are independently selected from the group consisting of xe2x80x94H, xe2x80x94OH, xe2x80x94C1-10 alkyl, xe2x80x94C6-14 aryl, and xe2x80x94C6-14 aryl-C1-3.
The conversion of the compound of Formula II to the compound of Formula I as provided by the invention is shown in Scheme III. 
Preferably, the semi synthetic statin of Formula I, synthesized by the method of the invention contains less than about 0.1% impurities.
Optionally, the semisynthetic statin of Formula I may be synthesized from an impure mixture a statin of Formula II comprising as much as about 30% impurities.
Preferably, R1 is an acyl group of the form 
wherein OM is the oxygen which is the hexahydronaphthalene ring substituent at position 8, R5 is selected from the group consisting of xe2x80x94C1-15 alkyl, xe2x80x94C3-15 cycloalkyl, xe2x80x94C2-15 alkenyl, xe2x80x94C2-15 alkynyl, -phenyl and -phenyl C1-6 alkyl and A is a substituent of R5 selected from the group consisting of hydrogen, a halogen, C1-6 alkyl, C1-6 alkoxy and C6-14 aryl.
Preferably, R2 is an acyl group of the form 
wherein OM is the oxygen which is the hexahydronaphthalene ring substituent at position 8, R6 is selected from the group consisting of xe2x80x94C1-15 alkyl, xe2x80x94C3-15 cycloalkyl, xe2x80x94C2-15 alkenyl, xe2x80x94C2-15 alkynyl, -phenyl and -phenyl C1-6 alkyl and B is a substituent of R6 selected from the group consisting of hydrogen, a halogen, C1-6 alkyl, C1-6 alkoxy and C6-14 aryl.
The dotted lines at X, Y and Z of Figure I and Figure II represent possible double bonds, the double bonds, when any are present, being either X and Z in combination or X, Y or Z alone.
Preferably, the lactone ring opening step is performed by reacting the lactone ring with ammonia, a primary amine, or a secondary amine. The lactone ring opening step may be performed by reacting the lactone with an amine selected from the group consisting of n-butylamine, cyclohexylamine, piperidine and pyrrolidine.
Preferably, the lactone ring opening is performed in an organic solvent. The organic solvent may be selected from toluene, cyclohexane, tetrahydrofurane, and acetonitrile.
Preferably, the lactone ring opening step is performed at a temperature above ambient temperature. Preferably the lactone ring opening step may be performed at a temperature of about 60xc2x0 C.
Preferably, the lactone ring opening step includes removing unreacted amine after forming the amid. Methods for removing the unreacted amine include removing the amine by evaporation and/or washing an organic solution containing the amid with dilute acid.
The present invention also provides for a process for protecting 1,3-diol moiety with a protecting group. Methods for protecting hydroxyl groups are well known in the art and are disclosed for example in U.S. Pat. Nos. 6,100,407, 6,252,091, European Patent EP 299656, and WO 95/13283 incorporated herein by reference. The protecting group may be selected from the group which consists of an acetal, a ketal, a cyclic sulfate, a cyclic phosphate and a borate group.
In one embodiment of the present invention, the protecting group may be a ketal. The process of protecting the 1,3 diol may be performed by forming the ketal using a ketone. Ketal formation is optionally performed in an organic solvent. The organic solvent may be selected from the group which includes toluene, cyclohexane, tetrahydrofurane, acetonitrile, and ethyl acetate.
In an alternative embodiment, the protecting group may be an acetal. The process of protecting the 1,3 diol may be performed by foming the acetal using an aldehyde. Acetal formation is optionally performed in an organic solvent. The organic solvent may be selected from the group which includes toluene, cyclohexane, tetrahydrofurane, acetonitrile, and ethyl acetate.
In an alternative embodiment, the 1,3 diol may be protected by formation of a dioxane moiety to protect the 1,3-diol as shown in Scheme IV. 
In an alternative embodiment, the 1,3-diol may be protected by formation of an acetal defined as 
wherein Rc may be selected from the groups comprising hydrogen, halogen, C1-6 alkyl-, C1-6 alkoxy, C6-14 aryl as for instance phenyl or aromatic heterocycle and m, n, are each independently 0-10.
The present invention also provides for protective groups, such as for instance: 
Preferably the protecting step is performed at a temperature from about 5xc2x0 C. to about 50xc2x0 C. Most preferably, the protecting step is performed at from about 20xc2x0 C. to about 25xc2x0 C.
Preferably, the protecting step is performed in the presence of a catalytic reagent. The catalytic reagent is preferably an acid. The acid may be selected from the group which consists of p-toluene sulfonic acid and sulfuric acid.
In one embodiment, the step of removing R1 includes reducing the statin of Formula III with a reducing agent. The reducing agent may be selected from the group consisting of lithium aluminum hydride, aluminum hydride and diisobutylaluminum hydride. The reduction step is preferably performed in an inert solvent. The inert solvent may be selected from the group consisting of toluene and tetrahydrofuran. The reduction step may further include neutralizing the remaining reducing agent with water.
The reduction step is preferably performed at a temperature of about 0xc2x0 C. to about 30xc2x0 C. The reduction step is preferably performed at a temperature of about 5xc2x0 C. to about 10xc2x0 C.
In one embodiment the process of removing R1 may includes reacting the statin of Formula III with an organometallic reagent in an inert solvent.
The organometallic reagent may be a Grignard reagent. The temperature of reacting the statin of Formula III with the Grignard reagent is preferably performed from about xe2x88x9210xc2x0 C. to about 20xc2x0 C. Preferably, the temperature of reacting the statin of Formula III is from about xe2x88x925xc2x0 C. to about 10xc2x0 C.
Alternatively, the organometallic reagent may be an alkyl lithium derivative. The alkyl lithium reagent is preferably n-butlylithium. The temperature of reacting the statin of Formula III with the alkyl lithium is preferably from about xe2x88x9270xc2x0 C. to about xe2x88x9220xc2x0 C.
In one embodiment of the invention, the step of removing R1 includes reacting the statin of Formula III with an amine. Preferably, the amine may be ammonia or a primary amine. Preferably, the molar ratio of the amine to Formula III may be about 1:1. Alternatively, the molar ratio of the amine to Formula III may be greater than about 1:1.
The step of removing R1 may be performed in the presence of water. The step of removing R1 may also be performed in the presence of an organic solvent.
Preferably, the step of removing R1 is performed at a temperature of from about 100xc2x0 C. to about 250xc2x0 C. More preferably, the step of removing R1 is performed at a temperature from about 130xc2x0 C. to about 200xc2x0 C.
Preferably, the step of removing R1 is performed at a pressure greater then atmospheric pressure.
In a preferred embodiment, the step of attachment of R2 includes acylation of the oxygen which is a hexahydronaphthalene ring substituent at position 8. The acylation step may include reacting the statin of Formula IV with an acid chloride. Alternatively, the acylation step may include reacting the statin of Formula IV with a free acid in the presence of carbodiimide. The carbodiimide may be 1,3 dicyclohexylcarbodiimide. In a further alternative embodiment, acylation may include reacting the statin of Formula IV with a symmetric anhydride in the presence of an organic solvent and a catalyst. Preferably, the catalyst is 4-dimethylaminopyridine.
Preferably, the acylation is performed at a temperature from about 20xc2x0 C. to about 110xc2x0 C. More preferably, the acylation is performed at a temperature from about 80xc2x0 C. to about 110xc2x0 C.
When the process of the invention includes protecting hydroxyl groups xe2x80x94O1H and xe2x80x94O2H, the process of the invention may further comprise removing the protecting groups after the step of the attachment of R2. Preferably, removing the protecting groups includes hydrolysis in a mixture of water and organic solvent in the presence of a catalyst. Preferably, the organic solvent is tetrahydrofuran. The catalyst may be an acid catalyst. The acid catalyst is preferably selected from the group which includes hydrogen chloride, sulfuric acid, and p-toluene sulfonic acid.
The step of removing the protecting groups is preferably performed at a temperature of from about 20xc2x0 C. to about 100xc2x0 C. More preferably step of removing the protecting groups is performed at a temperature of from about 30xc2x0 C. to about 70xc2x0 C.
The step of conversion of the amid to the acid salt preferably includes hydrolysis. The hydrolysis may be performed in a solution which includes a base, water and an organic solvent. The base is preferably selected from the group which includes sodium hydroxide and potassium hydroxide. The organic solvent is preferably selected from the group which includes methanol, ethanol, toluene, and tetrahydrofuran.
Preferably, the step of conversion of the amid to the acid salt includes forming a salt with a pharmaceutically acceptable counterion. The salt with the pharmaceutically acceptable counterion is preferably an ammonium salt.
Preferably, the step of lactone ring closing includes lactone formation in an organic solvent. The organic solvent is preferably selected from the group which consists of toluene, ethyl acetate, and cyclohexane. The lactone ring closing is preferably performed at an elevated temperature. The elevated temperature is preferably from about 60xc2x0 C. to about 110xc2x0 C. Most preferably the elevated temperature is from about 80xc2x0 C. to about 110xc2x0 C.
An alternative embodiment includes isolating the statin of Formula I by crystallization.
A Pharmaceutical Composition Containing Simvastatin
According to another aspect, the present invention relates to a pharmaceutical composition comprising the highly purified simvastatin disclosed herein and at least one pharmaceutically acceptable excipient. Such pharmaceutical compositions may be administered to a mammalian patient in a dosage form.
The dosage forms may contain substantially pure simvastatin or, alternatively, may contain substantially pure simvastatin as part of a composition. Whether administered in pure form or in a composition, the substantially pure simvastatin may be in the form of a powder, granules, aggregates or any other solid form. The compositions of the present invention include compositions for tableting. Tableting compositions may have few or many components depending upon the tableting method used, the release rate desired and other factors. For example, compositions of the present invention may contain diluents such as cellulose-derived materials like powdered cellulose, microcrystalline cellulose, microfine cellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropylmethyl cellulose, carboxymethyl cellulose salts and other substituted and unsubstituted celluloses; starch; pregelatinized starch; inorganic diluents such calcium carbonate and calcium diphosphate and other diluents known to one of ordinary skill in the art. Yet other suitable diluents include waxes, sugars (e.g. lactose) and sugar alcohols like mannitol and sorbitol, acrylate polymers and copolymers, as well as pectin, dextrin and gelatin.
Other excipients contemplated by the present invention include binders, such as acacia gum, pregelatinized starch, sodium alginate, glucose and other binders used in wet and dry granulation and direct compression tableting processes; disintegrants such as sodium starch glycolate, crospovidone, low-substituted hydroxypropyl cellulose and others; lubricants like magnesium and calcium stearate and sodium stearyl fumarate; flavorings; sweeteners; preservatives; pharmaceutically acceptable dyes and glidants such as silicon dioxide.
Dosage forms may be adapted for administration to the patient by oral, buccal, parenteral, ophthalmic, rectal and transdermal routes. Oral dosage forms include tablets, pills, capsules, troches, sachets, suspensions, powders, lozenges, elixirs and the like. The highly purified form of simvastatin disclosed herein also may be administered as suppositories, ophthalmic ointments and suspensions, and parenteral suspensions, which are administered by other routes. The most preferred route of administration of the simvastatin of the present invention is oral.
Capsule dosages will contain the solid composition within a capsule which may be coated with gelatin. Tablets and powders may also be coated with an enteric coating. The enteric-coated powder forms may have coatings comprising phthalic acid cellulose acetate, hydroxypropylmethyl cellulose phthalate, polyvinyl alcohol phthalate, carboxymethylethylcellulose, a copolymer of styrene and maleic acid, a copolymer of methacrylic acid and methyl methacrylate, and like materials, and if desired, they may be employed with suitable plasticizers and/or extending agents. A coated tablet may have a coating on the surface of the tablet or may be a tablet comprising a powder or granules with an enteric-coating.
The currently marketed form of simvastatin is available as a 5 mg, 10 mg, 20 mg, 40 mg, 80 mg tablet which includes the following inactive ingredients: magnesium stearate, starch, talc, titanium dioxide, and other ingredients. Butylated hydroxyanisole is added as a preservative.
Lovastatin is supplied as 10 mg, 20 mg, and 40 mg tablets for oral administration. In addition to the active ingredient lovastatin, each tablet contains the following inactive ingredients: cellulose, lactose, magnesium stearate, and starch. Butylated hydroxyanisole (BHA) is added as a preservative.
The function and advantage of these and other embodiments of the present invention will be more fully understood from the examples below. The following examples are intended to illustrate the benefits of the present invention, but do not exemplify the full scope of the invention.